I'm not so sure they're a bad artifact though. If you start from the premise that you should be allowed to enter an IP address as a URL, and consider that in fact an IP address is defined as an unsigned 32-bit integer, then it sort of makes sense to allow it. After all, dotted quad notation was simply an easier way to write the 32-bit integer...
RFC 1738 says in section 3.1:
host The fully qualified domain name of a network host, or its IP address as a set of four decimal digit groups separated by ".".
I think you -- or rather, your users -- may be out of luck. :-(
Nick Hilliard Ireland On-Line System Operations